More than 100,000 of those arrested in May were unaccompanied children or migrants traveling as a family when they arrived at the border, officials said. In March 2017, shortly after Mr. Trump took office, that number was about 2,000, according to government records.
“We are at a full blown emergency,” said John Sanders, the acting commissioner of Customs and Border Protection. “I cannot say this stronger: the system is broken.”
Mr. Trump has pushed ahead with the tariff threat against Mexico despite the concerns of some of his advisers, who warned that the measure might derail the effort to finalize his new North American trade deal. The president’s son-in-law, Jared Kushner, who negotiated some of the deal’s provisions with Mexico, had raised concerns about the potential impact on the United States-Mexico-Canada Agreement, as had Mr. Lighthizer and Steven Mnuchin, the Treasury secretary.
But they were opposed by advisers like Mr. Navarro and Stephen Miller, a chief policy adviser, and they were overruled by the president, who argued that tariffs had previously worked to pressure the Mexicans on immigration.
The threat has rattled financial markets and prompted an outcry from businesses that would be affected, including automakers, agricultural companies and retailers. The chairman of the Federal Reserve said on Tuesday that the central bank was watching Mr. Trump’s trade war warily and would act to prevent economic damage from the conflict.
Mr. Trump has made heavy use of tariffs on trading partners from China to Europe, but imposing tariffs on Mexico, the United States’ largest trading partner, would be a significant escalation in the president’s trade war. Mexico is a key supplier of products like fresh tomatoes and grapes; bluejeans; televisions; medical devices; and automobiles. Many companies have created supply chains that snake back and forth across the border — meaning some companies could be forced to pay Mr. Trump’s tariff multiple times as their products travel from farms to factories to consumers.
Businesses are also worried that the president’s move risks derailing what would be his signature trade achievement: passing the newly negotiated North American trade agreement.